The present invention relates to disk drive storage devices and in particular to ensuring continued usability of such devices.
In a dedicated servo design disk drive, servo information is written on one disk surface, with the other disk surfaces containing data written on tracks. A servo transducer senses the servo information.
Data transducers are moved to tracks of data as a function of the servo information. The data transducers must be located substantially over the tracks of data in order to read the data. Radial shift of the data transducers with respect to the transducer sensing the servo information causes the data transducers to not be located substantially over the tracks of data. Data tracks therefore appear to shift with respect to their expected positions. Data may be lost when such shifting occurs, and in any event, time is wasted trying to locate the data. Replacement of the disk/head assembly may be required.
The shift of transducers and data tracks is caused by a number of factors, many of the interrelationships of which are not well understood or controllable. Some of the causes include time and temperature induced changes in transducer suspension and support, radial run out of spindles on which the disks are mounted, bearing wear, disk clamping, and warp of spindle caused by drive mechanisms. Correction of one of the above causes may result in increased contribution to the transducer misalignment from the other causes.
When the number of read errors increases in a file, the user presently has several options. The user can continue to use the file and accept the errors, or the user can off load all the data in the file to an independent storage device and have the misalignment corrected by replacement of major assemblies. This exposes all of the data to mishandling and potential loss.
One method of determining the center of a track of data is discussed in U.S. Pat. No. 4,485,418 to Bremmer. The amplitude of a signal from the transducer is measured as the transducer is moved to each side of the track and compared to a predetermined reference level. The transducer can then be moved to the center of the track using an offset capability. This requires time, which reduces the average seek time of the disk drive. It also does not alleviate the problem of warpage of the spindle or other causes wherein the track of data is misaligned with the servo information.